1. Field of the Invention
The subject matter disclosed generally relates to the field of semiconductor image sensors.
2. Background Information
Photographic equipment such as digital cameras and digital camcorders may contain electronic image sensors that capture light for processing into still or video images, respectively. Electronic image sensors typically contain millions of light capturing elements such as photodiodes. The photodiodes are arranged in a two-dimensional pixel array.
FIG. 1 shows an enlarged cross-section of pixels in a pixel array of the prior art. The pixels include first regions 1 constructed from a first type of material, typically p-type, and second regions 2 constructed from a second type of material, typically n-type. The substrate and second regions 2 form p-n junctions of photodiodes. The p-n junctions are reverse biased to form depletion regions between dashed lines 3 and 4. The photons of incoming light 5 are absorbed to create electron-hole pairs 6. The electrons move to create an electrical current. The current is ultimately sensed and processed to reproduce the image detected by the image sensor.
Light at relatively long wavelengths penetrate deep into the photodiodes. Consequently, electrons are formed at the outer edges of the depletion regions. The depletion regions can grow and actually merge in region 7. The merger of depletion regions electronically couples the adjacent photodiodes in a capacitance manner. A change in voltage of a photodiode receiving light may vary the voltage in an adjacent photodiode not receiving light. This will result in an inaccurate sensing of light in the adjacent photodiode. It would be desirable to provide a pixel structure that would minimize the effects of lateral depletion region growth from impinging on adjacent depletion regions.